This invention relates to test systems, and more particularly to a testing device for evaluating armor material and ballistic fragments.
The evaluation of armor materials by using fragmenting munitions has long been difficult and expensive to perform under controlled conditions. A method traditionally used in armor testing and evaluation involved mounting a fragment simulator in a propellant casing, firing the projectile from a barrel at the test material, causing the projectile to pass through at least a pair of velocity-measuring screens, and then evaluating the resultant impact. After each individual firing, the system had to be refurnished before another fragment simulator could be launched. The use of the two screen velocity-measuring device made it mandatory that only one simulator could be launched with each firing. Thus, to evaluate any sizeable quantity of fragments and/or armor materials was extremely time consuming. Furthermore, the use of the fragment simulator, a bluntnose projectile, did not result in accurate test data truly representative of the damage behavior of actual munition fragments. In the search for test projectiles that would more closely duplicate the behavior of actual fragments, spherical, cubical and right cylindrical masses were used in place of the fragment simulators. These means, however, were not entirely satisfactory, and did not overcome the shortcomings inherent in the fragment simulator test system.
Efforts to use actual fragments resulted in the "arena" test method, wherein a munition shell was placed in the center of a circle of armor test materials, the shell detonated to spray a shower of fragments toward the circle of test material, and the armor damages evaluated. The disadvantages of this method far outnumbered the sole benefit of using actual, natural fragments. The probabilities of target impact by the fragments were haphazard and time penalties involved in this method are apparent. Since there was no way to collect, evaluate and categorize the fragments before the test, there were no means of assessing the effectiveness of the armor material against all types of fragments. Further, it was impossible to measure the velocity and mass of the fragments. Additionally, since the shell was statically detonated, the fragments did not have the initial velocity of a launched munition.
In another method involving the use of actual fragments, the fragments from an exploded munition were gathered and classified according to mass and shape. Then representative fragments were mounted in sabots and fired from gun barrels. The problems of cost, time consumption and data scatter inherent in this method are similar to those involved in the use of fragment simulations.
It is thus apparent that in the foregoing methods the use of actual fragments or fragment simulators produces data that is widely scattered, partial, or biased. Other problems are encountered in the use of actual fragments as test projectiles, including: (1) the cost and difficulty of obtaining and classifying the fragments; (2) problems with launching and maintaining the orientation of the fragments; (3) the lack of uniformity in fragment shape and size; and (4) the large scatter in fragment ballistic data. If these problems could be solved, actual fragments would be the test projectiles preferred over any fragment simulator or fragment model.
Closer equivalence to expected field performance of armor materials could be obtained if it were possible to project duplicate fragments against the material under consideration. Factory production of duplicates of actual fragments would result in uniformity of fragment shape and size, and the cost of production and variety of fragments could be closely controlled, thus resolving two of the foregoing problems associated with use of actual fragments. By analyzing the fragments from actual shells or other fragmenting munitions, it is possible to determine representative fragments or series of fragments from a particular shell or fragmenting munition. Selected fragments may then be reproduced by a suitable process, such as cold forging or precision molding. The mass and the area presented, or the ratio of these quantities (mass-to-area-presented, M.A.P.) can be closely controlled, so that in combination with the proper explosive the fragment velocity can be carefully monitored.
Use of an explosive producing a planar shock wave, such as a sheet explosive, as the propulsion system will result in fragment orientation very nearly that of the actual munition fragments without requiring the use of a launch barrel, considerably simplifying the launch problem. This simplification permits the test firing of a large number of fragments, which is a simple resolution of the large scatter in fragment ballistic data.
As with any testing procedure or apparatus, some permanent record of the test results must be made for later evaluation and analysis. The velocities and fragment quantities involved in armor materials testing compound the problem of recording the test results. Use of an accurately-timed, stroboscopic illumination source of precise duration and a still camera permits recording of the fragment trajectories on a single piece of film.